Field of the Invention
The present invention relates to mobile communication, and more particularly, to a method and device for handover between heterogeneous wireless communication technologies in a communication environment that supports a plurality of wireless networks.
Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. The 3GPP LTE adopts MIMO (multiple input multiple output) having maximum four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
FIG. 1 is a schematic diagram illustrating a structure of evolved mobile communication network.
As shown in FIG. 1, an evolved UMTS terrestrial radio access network (E-UTRAN) is connected to an evolved packet core (EPC).
The E-UTRAN includes base stations (or eNodeBs) 20 that provides a control plane and a user plane to a user equipment (UE). The base stations (or eNodeBs) 20 may be interconnected through an X2 interface.
The radio interface protocol layers between the UE and the base station (or eNodeB) 20 may be divided by L1 (a first layer), L2 (a second layer) and L3 (a third layer) based on lower three layers of open system interconnection (OSI) standard model that is widely known in communication systems. Among these layers, a physical layer included in the first layer provides an information transfer service using a physical channel, and a radio resource control (RRC) layer located at the third layer performs a role of controlling radio resources between the UE and the base station. For this, the RRC layer exchanges a RRC message between the UE and the base station.
Meanwhile, the EPC may include various elements. FIG. 1 shows a mobility management entity (MME) 51, a serving gateway (S-GW) 52, a packet data network gateway (PDN GW) 53 and a home subscriber server (HSS) 54 among the various elements.
The base station (or eNodeB) 20 is connected to the mobility management entity (MME) 51 of the EPC through an S1 interface, and is connected to the serving gateway (S-GW) 52 through an S1-U.
The S-GW 52 is an element that operates at a boundary point between a radio access network (RAN) and a core network and has a function of maintaining a data path between an eNodeB 20 and the PDN GW 53. Furthermore, if a user equipment (UE) moves in a region in which service is provided by the eNodeB 20, the S-GW 52 plays a role of a local mobility anchor point. That is, for mobility within an E-UTRAN (universal mobile telecommunications system (Evolved-UMTS) terrestrial radio access network defined after 3GPP release-8), packets can be routed through the S-GW 52. Furthermore, the S-GW 52 may play a role of an anchor point for mobility with another 3GPP network (i.e., a RAN defined prior to 3GPP release-8, for example, a UTRAN or global system for mobile communication (GSM) (GERAN)/enhanced data rates for global evolution (EDGE) radio access network).
The PDN GW (or P-GW) 53 corresponds to the termination point of a data interface toward a packet data network. The PDN GW 53 can support policy enforcement features, packet filtering, charging support, etc. Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor point for mobility management with a 3GPP network and a non-3GPP network (e.g., an unreliable network, such as an interworking wireless local area network (I-WLAN), a Code Division Multiple Access (CDMA) network, or a reliable network, such as WiMax).
In the network configuration of FIG. 1, the S-GW 52 and the PDN GW 53 have been illustrated as being separate gateways, but the two gateways may be implemented in accordance with a single gateway configuration option.
The MME 51 is an element for performing the access of a terminal to a network connection and signaling and control functions for supporting the allocation, tracking, paging, roaming, handover, etc. of network resources. The MME 51 controls control plane functions related to subscribers and session management. The MME 51 manages numerous eNodeBs 22 and performs conventional signaling for selecting a gateway for handover to another 2G/3G networks. Furthermore, the MME 51 performs functions, such as security procedures, terminal-to-network session handling, and idle terminal location management.
Meanwhile, recently, the high speed data traffic has been rapidly increased. In order to meet such traffic increase, technologies have been introduced for offloading the traffic of UE to WLAN (Wi-Fi) or a small cell.
FIG. 2 is a schematic diagram illustrating a network structure to which a small cell or a WLAN AP is added.
Referring to FIG. 2, within the coverage of a base station 31 for the small cell, a plurality of WLAN AP may be arranged. That is, several radio access technologies (RATs) are existed around a UE. Accordingly, the UE may distribute data traffic into the several RATs. The base station 31 for small cell may be arranged within the coverage of a macro base station such as the existing eNodeB.
As known from by reference to FIG. 2, the P-GW 53 and the HSS 54 are connected to an access authentication authorization (AAA) server 56. The P-GW 53 and the AAA server 56 may be connected to an evolved packet data gateway (ePDG) 57. The ePDG 57 plays a role of a security node for not being trusted non-3GPP network (e.g., WLAN or Wi-Fi, etc.). The ePDG 57 may be connected to a WLAN access gateway (WAG) 58. The WAG 58 may be in charge of a role of P-GW in Wi-Fi system.
In this way, when an existing mobile communication network and a heterogeneous network are coupled, handover between heterogeneous networks may be performed.
FIG. 3 is a control flowchart illustrating time delay in a control plane upon performing handover between heterogeneous networks.
As shown in FIG. 3, transmission and reception of beacon and data between an UE and an AP (WiFi AP) is performed using a wireless LAN (WiFi). That is, the UE performs wireless communication through the wireless LAN (S310).
The UE may determine handover to another wireless communication network when intensity of a transmitted and received signal becomes weak or according to a load of a transmitted and received signal (S320).
Because intensity of a signal is not changed and because there is no large change in a load of a transmitted and received signal, when communication can be continued through the wireless LAN, it is determined that the UE does not perform handover and the UE maintains communication with the WiFi AP (S330).
However, when it is impossible to maintain communication through the wireless LAN with weakening of intensity of a signal or with increase in a load of a transmitted and received signal, the UE may determine handover to another wireless communication network (S340).
When handover is determined, connection between the UE and the WiFi AP is disassociated (S341), and the UE attempts connection to a base station, for example a EUTRAN eNB for connection to a heterogeneous communication network.
When the UE receives a synchronization signal from the EUTRAN eNB and is synchronized with the EUTRAN eNB (S342), the UE transmits a random access channel (RACH) preamble to the EUTRAN eNB (S343), and the EUTRAN eNB transmits a RACH response to the UE (S344).
When random access is established, the UE requests Radio Resource Control (RRC) connection to the EUTRAN eNB (S345), and the EUTRAN eNB transmits an RRC connection setup to the UE in response thereto (S346).
The UE transmits an RRC connection setup complete message including a service request to a core network to the EUTRAN eNB (S347). Thereby, wireless network connection is established between the UE and the EUTRAN eNB, and the UE and the EUTRAN eNB maintain an RRC connection state.
As shown in FIG. 3, about 12 ms is consumed in transmission and reception of an RACH signal, and about 19.5 ms is consumed in wireless connection between the UE and the EUTRAN eNB.
The EUTRAN eNB, having received a service request from the UE transmits a service request message to the MME (S348).
When the service request is received, the MME may determine whether the UE, having requested the service is an authenticated UE and transmit an initial context setup request message including an MME UE S1AP ID, an eNBUE S1AP ID, an UE Aggregate Maximum Bit Rate, an E-RAB ID, a QoS parameter, an S-GW address, an S1 S-GW TEID, and a Security Key to the EUTRAN eNB (S349).
The EUTRAN eNB, having received the initial context setup request message sets data bearer based on context information within the corresponding message and transmits an RRC connection reconfiguration message including setup information of data bearer to the UE (S350).
When data bearer setup is complete, the EUTRAN eNB transmits an initial context setup response to the initial context setup request message to the MME (S351). Such a Non Access Stratum (NAS) message between the MME and the UE is transmitted and received through backhaul, and about 38 ms is consumed in transmission and reception of the NAS message after wireless connection is performed between the UE and the EUTRAN eNB.
In this way, upon performing handover between heterogeneous networks, time delay consumed in a control plane is about 69.5 ms. When it is assumed that communication between the UE and the EUTRAN eNB and between the EUTRAN eNB and the MME is smoothly performed and that there is no failure in transmission and reception of an RACH signal for RRC connection, such time delay may occur and be regarded as a minimum time consumed in a control plane upon performing handover.
Further, when dataflow corresponding to data bearer generated through initial context setup do not correspond with data flow in which the UE is to hand over from Wi-Fi to a cellular network, the UE should request data bearer setup of data flow to hand over to the cellular network through a public data network (PDN) connection request message to the MME. When such a procedure is performed, a time consumed in a control plane additionally increases upon performing handover between heterogeneous networks.
When a processing time between the UE and the MME and a NAS message transmission and reception time may be simplified upon performing handover, i.e., when a process of steps S348 to S351 may be shortened, time delay to be required upon performing handover will be able to also reduce.
FIG. 4 is a control flowchart illustrating time delay of a user plane upon performing handover between heterogeneous networks.
When data bearer is set, the UE may transmit UL data to the EUTRAN eNB (S410), and the EUTRAN eNB transmits the UL data to an S-GW and a P-GW (S420 and S430).
When there is no scheduling delay, as shown in FIG. 4, upon performing handover between heterogeneous networks, time delay consumed in a user plane is about 26 ms.
In short, when the UE performs handover to LTE, which is a heterogeneous network while performing communication through the wireless LAN, a time consumed in a control plane for network connection is 69.5 ms, and a time consumed in a user plane for data uplink is 26 ms, and total time delay is about 95.5 ms.
Table 1 represents quality control information (QCI) required per service.
TABLE 1PacketPacketDelayError LossResourceBudgetRateQCITypePriority(NOTE 1)(NOTE 2)Example Services1GBR2100 ms10−2Conversational Voice(NOTE 3)24150 ms10−3Conversational Video (Live Streaming)(NOTE 3)33 50 ms10−3Real Time Gaming(NOTE 3)45300 ms10−6Non-Conversational Video (Buffered Streaming)(NOTE 3)5Non-GBR1100 ms10−6IMS Signalling(NOTE 3)66300 ms10−6Video (Buffered Streaming)(NOTE 4)TCP-based (e.g. www, e-mail, chat, ftp, p2p filesharing, progressive video, etc.)77100 ms10−3Voice,(NOTE 3)Video (Live Streaming)Interactive Gaming88300 ms10−6Video (Buffered Streaming)(NOTE 5)TCP-based (e.g , www, e-mail, chat, ftp, p2p file99sharing, progressive video, etc.)(NOTE 6)
As shown in Table 1, because packet delay of QCI 3 is 50 ms, when following time delay occurring in current handover, packet delay requirements of QCI 3 may not be satisfied.
Further, in a case of QCI 1, 5, and 7 in which packet delay is 100 ms, packet delay requirements may not be satisfied according to a load of a wireless network or a core network and additional PDN connection request execution.
Further, a new service such as realistic communication technology and tactile Internet requiring packet delay of about 1 ms, and remote medical or remote control requiring packet delay of about 40 m requires packet delay smaller than that of an existing service.
Therefore, as described above, upon performing handover between heterogeneous networks, shortening of a delay time is required.